1. Field of the Invention
The embodiment discussed herein is related to an optical device that includes multiple optical components arranged in fixed positional relation, and an imaging apparatus that includes the optical device.
2. Description of the Related Art
In recent years, with demands for size reductions of various kinds of apparatuses having imaging functions (hereinafter, “imaging apparatus”), there has been a tendency for the size of optical components to be reduced, such as lenses, or optical devices (optical systems) that are constituted by a multiplicity of optical components. Moreover, for small imaging apparatuses such as mobile telephones and compact cameras, there has been a trend toward imaging devices having more pixels, and with increased pixels of imaging devices, optical apparatuses that are compact and highly precise are demanded.
For example, if a method of assembling optical components at determined positions in a lens barrel by insertion with minimal positioning adjustments is applied, by narrowing the tolerance for respective optical components, the optical components can be assembled with high precision. On the other hand, if the tolerance for the optical components is narrowed, production of the optical components decreases, reducing yields at mass production of optical devices or imaging apparatuses incorporating the optical devices. Moreover, when such a method is applied, the precision (optical performance) of the optical devices depends on the manufacturing precision of components, and therefore, if the tolerance is eased to improve mass production, the precision (optical performance) of the optical devices declines.
For resin products formed using a resin material by injection molding, relatively high manufacturing precision can be maintained with increased accuracy in molding techniques and improvement in precise molding techniques. Therefore, a technique to achieve precision (optical performance) for optical devices when a method of assembling by insertion is applied has conventionally been used in which a positioning structure is provided in a resin optical component to position another optical component, and positioning of the other optical component is performed using this positioning structure.
Moreover, a technique to achieve demanded precision (optical performance) of an optical device by core adjustment has been used conventionally in which optical components related to the optical performance are adjusted based on a reference optical member at assembly of the optical device, for example. Core adjustment is effective when optical components are made from glass, such as lenses formed using a glass material by glass molding.
For glass optical components that are formed using a glass material by glass molding or the like, because it is difficult to achieve high decentration precision with a single glass optical component, core adjustment is required at assembly of an optical system. For example, when a resin lens and a glass lens are both present in an optical device such as a lens unit, the size of which is decreased by directly connecting lenses, by performing core adjustment of the glass lens relative to the resin lens, manufacturing precision of which is high, positional relation between the resin lens and the glass lens is adjusted.
In addition, for glass optical components, because it is difficult to achieve manufacturing precision with a single optical component, it is difficult to provide a positioning structure with high precision to glass optical components. Therefore, for example, when a resin lens and a glass lens are both present, core adjustment is performed using a jig for core adjustment. After core adjustment is performed, positional relation between the resin lens and the glass lens is fixed using adhesive to cement the lenses, for example (for example, Japanese Patent Laid-open Publication No. S63-269323).
For example, a technique of fixing a resin lens and a glass lens using UV curing adhesive has conventionally been used. The UV curing adhesive is applied by potting or the like in the state where positional relation between the resin lens and the glass lens is fixed by a jig for core adjustment. The jig for core adjustment is removed after radiating UV light on the applied adhesive to finish primary curing of the UV curing adhesive. The lenses from which the jig for core adjustment is removed are kept in such a place that secondary curing is promoted, or the like.
Furthermore, a technique of fixing optical components that are inserted in an optical path of an optical pick-up to a base member to which other optical elements are attached, through a holding member that is formed using a material whose linear expansion coefficient is different from that of the base member has conventionally been used (for example, Japanese Patent Laid-open Publication No. H7-210892).
However, in the above conventional technique, if optical components to be fixed to each other by adhesive have different linear expansion coefficients, the degree of expansion caused by a change in the ambient temperature is different between the lenses. If the degree of expansion of the respective lenses differs from each other, compressive stress or stress in a direction of pulling outwards acts on the portion of the adhesive, and the adhesive can deform. If the adhesive deforms, the positional relation between the optical components may change, or the optical components may be contorted to result in degradation of the optical performance.
Deformation of the adhesive becomes significant as changes in the ambient temperature occur repeatedly. As deformation of the adhesive becomes more significant, a change in positional relation between the optical components or contortion of the optical components occurs significantly. Accordingly, as changes in the ambient temperature occur repeatedly, degradation of the optical performance is significant. Problems originating from differences in the linear expansion coefficients of components fixed to each other may occur also with the technique disclosed in Japanese Patent Laid-open Publication No. H7-210892. Further, with this technique, there is another problem that core adjustment cannot be performed.
Moreover, with the conventional technique in which the jig for core adjustment is removed after primary curing of UV curing adhesive, because UV curing adhesive contracts until cure is complete even after primary curing, the positional relation between the resin lens and the glass lens changes due to adhesive contracting during secondary curing. A change in positional relation between the optical components may result in degradation of the optical performance of the optical device.
As a countermeasure against this problem, if the jig for core adjustment is removed after secondary curing is completed, assembly work cannot be proceeded for long time until the jig is removed, and yields in mass production of optical systems, i.e., optical devices or imaging apparatuses including the optical system, is reduced. In addition, a place to store lenses to which the jigs for core adjustment are attached for long time must be prepared, and this may cause increased manufacturing cost.